In recent years, wireless chips for wireless data transmission/reception are actively developed. The wireless chip for data transmission/reception is called an IC chip, an RF tag, an RFID, a wireless tag, an electronic tag, a wireless processor, a wireless memory and the like, and most of the wireless chips which are currently in practical use are formed using a silicon substrate.
Such a wireless chip is attracting attention as an alternative to a barcode having a small amount of data so as to be used for merchandise management (see Patent Document 1). In addition, a contactless IC card having a high security function is also attracting attention in order to prevent the counterfeiting or unauthorized use.
FIG. 23 shows an example of a conventional configuration of such a wireless chip. Shown in FIG. 23 is a wireless chip which reads and writes data from/to a memory in accordance with an instruction received. A wireless chip 201 includes an antenna circuit 202, a power source circuit 203, a demodulation circuit 204, a modulation circuit 205, a memory IF 206 and a memory 207.
The antenna circuit 202 receives electromagnetic waves and generates AC signals. The power source circuit 203 rectifies the AC signals and generates power to be supplied to other circuits. Each of the demodulation circuit 204, the modulation circuit 205, the memory IF 206 and the memory 207 extracts an instruction or data from the AC signal received, reads and writes data from/to a memory in accordance with the decoded instruction, and transmits the result.
[Patent Document 1]
Japanese Patent Laid-Open No. 2003-123033
In the invention, a wireless chip called an RFID, a contactless IC card, an ID tag, an ID card or the like is collectively called an ID chip. The size of such an ID chip is often determined according to an antenna circuit thereof. In general, power source voltage or power supplied to an ID chip can be more easily received with a larger antenna. On the other hand, it is less easily received with a smaller antenna, thereby the communication distance becomes shorter. For example, an ID chip of an electromagnetic induction type using a frequency band of 13.56 MHz can obtain, with an antenna having a size of a credit card, a communication distance of about 80 cm; however, it is decreased to about 1 cm with an antenna of about 5 mm square.
In this manner, when the antenna is downsized, the communication distance becomes shorter and the application thereof is limited accordingly; therefore, it is vital to improve the communication distance.
In view of the foregoing, it is a primary object of the invention to provide an ID chip capable of data communication with a small antenna, namely a compact ID chip having an improved communicable distance.